Magnetic read/write heads are extensively used in computers and other applications in which data is written onto and read from a magnetic medium such as a magnetic tape or disk. In such applications, the magnetic head is mounted onto a suspension assembly arm which is computer controlled so that the head may be rapidly moved from position to position to write or read information from the portion of the medium specified by the computer.
The magnetic heads must be moved as rapidly as possible over the associated magnetic medium in order to minimize the time required for locating the correct track that is to be read or written. This rapid movement often produces acceleration and deceleration forces on the head in the order of 40 gs. Magnetic disks are manufactured with an extremely high degree of flatness. The magnetic heads float on a very thin film of air just above the disks. Each magnetic head is secured to a resilient suspension assembly arm in order to obtain the mobility which permits the head to float on the air film and to provide a resilient load which exerts an accurately defined pressure on the head. In some usages, a plurality of disks and associated heads are used to provide extra data storage capacity. In order to minimize the external dimensions of these storage devices, the disks are typically arranged as closely as possible to each other. The suspension arm and associated heads therefore are spaced between two magnetic disks and should be as flat as possible and operate as close as possible to the surface of the disk with which each head cooperates. It is obvious that the suspension arm should never touch the magnetic disk surface because this would render the disk unserviceable.
The current trend in the industry is towards higher and higher areal recording densities and an ever increasing numbers of tracks on the associated disks. This has led to increased miniaturization of all parts of the recording apparatus including the heads and the apparatus to which the heads are attached. As a result, thin film heads are currently used that have dimensional tolerances in the order of several millionths of an inch. This requires that the heads be accurately positioned on the associated suspension arm so that the head may operate parallel to the plane of assembly arm as well as the plane of the disk with which it is to exchange data. In practice, the head must be positioned parallel to the plane of the disk within several thousandths of an inch in each dimension. The head must also have a minimal rotational error with respect to the magnetic orientation of the data to be read. The head must be separated from the moving disk by no more than several millionths of an inch.
It can be seen from the above that the positioning of a head on a suspension arm is extremely critical regarding the tolerances that must be achieved if the optimum operation of the head is to be achieved. The close tolerances and accurate positioning requires that heads be positioned with extreme precision on suspension assembly arms during the fabrication operation of these elements.
It is presently a problem to position heads with the required precision on suspension assembly arms. The typical procedure used to affix a head to a suspension arm is to position the suspension arm in a first tool holder. The head is placed in a second tool holder and the two tool holders are then moved a controlled manner so that the end of the suspension arm and the head are brought together with the required orientation. The head is then permanently affixed to the end of the suspension arm by use of a suitable adhesive or the like. This procedure has inherent problems since the accuracy by which the head is positioned on the arm is dependent upon a number of variables. These include, the dimensional accuracy of the head, the accuracy of the tool that holds the arm, the accuracy of the tool that holds the head, the accuracy of the apparatus that moves the head over the arm, and finally the accuracy of the apparatus that lowers the head onto the arm. In this positioning operation, it is necessary that the geometric center of the head be positioned with precision over a predetermined point on the assembly arm with an error of no more than plus or minus one mill in any direction and with an error of only several minutes of a degree with respect to the rotational position of the head with respect to the plane of the top surface of the assembly arm. Although the design objectives are plus or minus one mill, in a typical production line, there can be an error of five mills due tolerances of the head and the apparatus used to position the head on the suspension arm. An error of in excess of two mills can cause operational problems that require head-arm assemblies having errors in excess of this amount to be discarded.
It can therefore be seen that it is currently a problem to affix a magnetic head with the required precision on suspension assembly arm so that the head will have the correct orientation with respect to the disk with which it is to exchange data.